Superman, one of the "New Gods" or one of Supes' villains like Doomsday, Darkseid etc would be closest in terms of strength.
On a related note, although Clayface isn't as strong as Hulk, I could see him being able to take him down if he used the right tactics (Clayface's amorphous body renders Hulk's strength and grip useless).

"on clayface" the reason i hate these arguments so much is due to the fact the hulks strength is such a variable. for instance at the end of world war hulk he got so mad his voice shattered all the windows in Manhattan and a step (note the word step as in walking) split the island in two

I was going off of just transformed strength, but I agree that the hulk's strength is annoying in its inconsistency. It probably came about after the writers wrote themselves into a corner and the only way for the hulk to beat a certain bad guy was to make it so that he gets stronger as he gets angrier.